Download Nephrops off Horns Reef (FU33), Demersal otter trawl

Nephrops off Horns Reef (FU33), Demersal otter trawl
Nephrops off Horns Reef (FU33), Demersal
otter trawl
Content last updated
27th Jan 2016
Stock:
Nephrops off Horn's Reef, Functional Unit 33
Management:
EU
Overview
The Norway Lobster (Nephrops norvegicus) is a decapod crustacean distributed throughout the North East Atlantic from Iceland and
northwest Norway, to the Atlantic coast of Morocco and the western and central Mediterranean. Nephrops construct burrows in muddy
seabed habitats in depths ranging from 20-800m, and emerge only to forage for food and to mate. Nephrops are only vulnerable to
fishing when outside their burrows.
Nephrops support extremely valuable fisheries and are caught mainly by demersal otter trawling. Off Horn’s Reef, FU33, is located in the
eastern North Sea offshore from the west coast of Denmark and supports a trawl fishery with vessels using a mixture of single and multirig Nephrops (codend mesh size 80 – 99mm), whitefish trawls (codend mesh size 100mm or over) and fixed gears. It was until 2005
fished almost exclusively by vessels from Denmark, however in recent years has also been fished by vessels from Germany, the
Netherlands and Belgium.
Mud patches with Nephrops populations are grouped into separate Functional Units (FUs) of which there are nine within the North Sea
(ICES Subarea IV): Moray Firth (FU9), Noup (FU10), Fladen Ground (FU7), Norwegian Deeps (FU32), Farn Deeps (FU6), Firth of Forth (FU8),
Botney Gut – Silver Pit (FU5), off Horn’s Reef (FU33) and Devil’s Hole (FU34). Although the stock in each FU is assessed separately, and ICES
gives advice on landings of Nephrops according to single-stock advice, a single TAC is set for the whole of Subarea IV.
Figure 1. Map showing stock range, (Source:
ICES 2012)
References
ICES. 2012. ICES Advice 2013, Book 6, 2012. 6.4.14.6 Nephrops off Horn’s Reef (FU33), pp. 44 – 48.
ICES. 2014. ICES Advice 2015. Book 6, 2014. 6.3.15.6 Nephrops off Horn’s Reef (FU33), pp. 43 – 47.
ICES. 2015. Report of the Working Group for the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK), 30 April–7
May 2014, ICES HQ, Copenhagen, Denmark. ICES CM 2014/ACOM:13. 1493 pp.
Catchpole, T.L, Frid, C.L.J., Gray, T.S. 2006. Importance of discards from the English Nephrops norvegicus fishery in the North Sea to
marine scavengers. Mar Ecol Prog Ser 136: 1–3
Stock Status
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Nephrops off Horn’s Reef, FU33 has been scored moderate risk. This is because Nephrops have a low vulnerability score of 14/100 and
have an unknown stock size (B) and harvest rate (F).
Management
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Nephrops off Horn’s Reef, FU33 has been scored moderate risk. This is because whilst the functional unit is assessed annually, as a
data-limited stock, by ICES, the TAC is set for Subarea IV as a whole, which can lead to uncontrolled increases in fishing effort in individual
functional units. Surveillance is generally moderately effective, though more effective on larger vessels. Compliance is considered
adequate with no officially reported problems.
Bycatch
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The bycatch risk of this fishery are scored very high risk. This is because the bycatch and reported discard rates are high (>50%) in
Nephrops trawls due to the small cod end mesh requirements of the target species. However, measures to reduce bycatch and discards
in these fisheries have been the subject of much research over the years, resulting in technical measures which improve selectivity, which
in turn have been implemented as a statutory requirement. Further measures, such as modified trawl designs, have been implemented
on a non-statutory basis.
Furthermore, the cod recovery plan has been implemented in this area and this is expected to have had an influence on the discarding
levels in North Sea demersal fisheries and the incoming EU landings obligation is also intended to reduce discarding.
Habitat
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The habitat risk of this fishery has been scored a moderate risk. This is because, with in the core area of this fishery there are
vulnerable marine habitats identified and currently there is some spatial management to avoid trawling affecting these habitats.
However, there remains some uncertainties about the location of some sensitive seabed habitats so these remain at risk.
Outlook
Stock
Current risk status
Outlook
Reason
Moderate
Stable
The stock status is unknown, however
catch rates are stable and harvest rates
are being set at levels well below the level
for maximum sustainable yield (FMSY).
Management
Moderate
Stable
The CFP is going through reform and
there is some uncertainty on how this will
impact fisheries management in the
North Sea. The Nephrops TAC applies to
all North Sea Functional Units combined
and does not protect specific FUs.
Bycatch
Very High
Improving
Bycatch of non-target species in this
fishery is relatively high with poor
selectivity. However, with technical and
spatial management measures
continuously under development and the
incoming EU landings obligation intended
to reduce discarding of managed species,
the bycatch risk is likely to reduce in the
future.
Habitat
Moderate
Improving
Nephrops otter trawls have the potential
to interact with vulnerable habitats, but
there is some spatial management with in
the footprint of this fishery which
provides protection to identified
vulnerable marine habitats. Management
measures are continuously being
developed and could reduce the risk
further.
Type
Stock
Management
Bycatch
Habitat
Current Risk Status
Outlook
Reason
Stock Status Details
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Time-trends
Landings were relatively low until 1996 at below 200 tonnes per year; they then showed a sharp general increase through to a peak of
1500 tonnes in 2007 but have generally fallen since then to an estimated 946 tonnes in 2013. The proportion of discards has not yet been
fully quantified for this area being estimated only from the Danish component of the fishery. The fishery has been and is currently a
100% trawl fishery however the relative contribution of TR1 trawlers (those with 100mm or higher mesh size otter trawls) and of TR2
trawlers (those with 80 – 99mm mesh size otter trawls) is unknown. With its offshore location, the predominance of landings are from
larger vessels.
Landings were until 2005 made up almost of entirely by those from Danish vessels, at over 90% for all years. They have since then steadily
converged in proportion with those from Dutch vessels, with both countries now contributing seeing approximately a third of the
landings. Half of the other third has grown to be comprised of landings by Germany and, despite some landings by UK vessels around
2008 reducing the share, the remaining portion has been landed by vessels from Belgium.
Stock size, as reported from underwater TV (UWTV) surveys, has been estimated using a proxy burrow density figure based on the lowest
density observed in the Fladen Ground (FU7) UWTV survey, which is then applied to a surface area of the off Horn’s Reef ground of
5700km2. At 0.20 burrows per square metre, this density is at the lower end of all burrow densities for all FUs, however when considered
for the entire surface area, the result is an estimate of stock size implying a harvest rate of 2.7%, well within the MSY level of 8%.
A stock size indicator using a landings per unit effort (LPUE) time series has only recently, from 2005, included data from the Netherlands,
but has shown landings per unit effort increase for Denmark while staying relatively stable for the Netherlands. Stable / increasing LPUE
indicates that a similar state is extant either for the state of the stock or of the efficacy of those vessels fishing it.
In absence of both stock size (B) and harvest rate (F) reference points, the population of Nephrops off Horn’s Reef is considered as
unknown and the stock status is stock is consequently then scored based on the fishbase vulnerability score of 14/100, indicating low
vulnerability.
Fig. 1& 2. Time series of landings (in tonnes)
and of a stock size indicator in landings per
kWday (of vessel power and time) off Horn’s
Reef FU33.
Fig. 1& 2. Time series of landings (in tonnes) and of a stock size indicator in landings per kWday (of vessel power and time) off Horn’s Reef
FU33.
Stock structure and recruitment
Nephrops require sediment with a silt & clay content of between 10 – 100% to excavate burrows, and the locations of suitable sediments
defines the distribution of the species. There are nine discrete populations in Subarea IV, referred to as functional units (FU), and these are
assessed as independent stocks. The off Horn’s Reef stock, FU33, inhabits an area of 5700km2 (ICES 2015). Changes in recruitment can
be inferred from trends in size compositions of catches, but there is no survey or assessment model to generate a time series of
recruitment indices.
Nephrops are omnivorous feeding on polychaetes, crustaceans, molluscs and echinoderms and are predated upon by large gadoids,
particularly cod, however generally low levels of cod in recent years have likely resulted in reduced predation.
Females mature at approximately 3 years of age, and during the egg incubation period they leave the burrows less frequently and
commercial catches become dominated by males. Larvae are pelagic for one month after hatching and after metamorphosis the small
Nephrops settle on the sea bed.
Data gaps and research priorities
An UWTV survey has not been carried out for this FU and without a reliable estimate of stock abundance, a harvest rate has been set
An UWTV survey has not been carried out for this FU and without a reliable estimate of stock abundance, a harvest rate has been set
based a data-limited approach using the average of the prior 10 years of landings. This harvest rate has taken into account a sensitivity
analysis that has examined the possibility of a lower burrow density of 0.1 burrows per square metre (half that of the proxy Fladen
Ground FU7 estimate at the time of the last assessment) with the current 2.7% advice is around half the MSY proxy that ICES uses for data
limited stocks. The implied harvest rate of 2.7% is highly likely to remain below the 8% threshold even if a high discard rate were included.
The population has not been well-studied and biological parameters such as growth are considered particularly uncertain. Discards are
only currently quantified for the Danish component of the fishery representing 33% of the landings and are quoted by ICES to be 34% by
weight, despite a figure of 33% by number then being referred to as a basis for the assessment. With the expectation that discarding will
typically be of smaller Nephrops, the latter figure is therefore be considered an underestimate of total discarding.
References
Catchpole, T.L, Frid, C.L.J., Gray, T.S. 2006. Importance of discards from the English Nephrops norvegicus fishery in the North Sea to
marine scavengers. Mar Ecol Prog Ser 136: 1–3
ICES. 2012. ICES Advice 2013, Book 6, 2012. 6.4.14.6 Nephrops in off Horn’s Reef (FU33), pp. 43 – 47.
ICES. 2014. ICES Advice 2015. Book 6, 2014. 6.3.15.6 Nephrops in the off Horn’s Reef (FU33), pp. 43 – 47.
ICES. 2015. Report of the Working Group for the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK), 30 April–7
May 2014, ICES HQ, Copenhagen, Denmark. ICES CM 2014/ACOM:13. 1493 pp.
Management Details
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TAC Information
Catch 2015 (t)
Advised Catch 2016 (t)
Agreed TAC 2016 (t)
Advised Catch 2017 (t)
Advised and Agreed Catches*
Landings 2013 (t)
Advised catch 2015 (t)
Agreed TAC 2015 (t)
Advised catch 2016 (t)
946**
1136t**
17843t***
1136t**
* advice for this FU is produced biennially and has not been updated this year
** Landings and catch advice do not include discards which are unknown
*** TAC is set for EC waters of the entire SubArea IV
Stock Harvesting Strategy
Scientists have devised an approach to estimate the abundance of Nephrops using a sledge with an underwater television (UWTV) camera
and lights which is towed by a research vessel across the mud patches in a Functional Unit. Burrows with characteristics indicating they
are occupied by Nephrops are counted to assess the number of burrows per square metre. For off Horn’s Reef, the assessment of
abundances is based on a proxy burrow density figure formed on the lowest density observed in the Fladen Ground (FU7) UWTV survey,
which is then applied to a surface area of the off Horn’s Reef FU of 5700 km2 and raised up to estimate the total stock abundance using
mapping techniques.
Nephrops off Horn’s Reef FU33 is assessed biennially to estimate biomass and fishing mortality in relation to reference points for
sustainability. The assessments use international landings and proxy figures for discards in conjunction with the TV survey. The reference
points are updated less frequently than the stock assessment and are calculated using the international catch data in conjunction with the
length-frequency data from monitoring at sea in in port.
The fisheries for Nephrops in the North Sea are managed under the EU Common Fisheries Policy (CFP) primarily through annual TACs
(Council Regulation (EC) 1380/2013) set for the North Sea as a whole. Nephrops otter trawls with mesh size 70-99mm are included in the
regulated TR2 gears subject to effort (kw-days) controls in relation to gear group, mesh size and catch composition specified in the EU long
term cod management plan since 2008 (Council Regulation (EC) 1342/2008 and 1243/2012).
These controls do not provide adequate safeguards to avoid depletion of Nephrops in any functional unit. Vessels are free to move
between grounds, subject to any specific access requirements, allowing effort to develop on some grounds in a largely uncontrolled way.
This has historically resulted in inappropriate harvest rates from some FUs.
Surveillance and Enforcement
Landings are monitored from EU logbooks and sales notes, or sales notes only for under 10m vessels that do not have to keep EU
logbooks. Discard rates and mean sizes of the Nephrops in this area are only partially monitored.
There are no specific EU or national management objectives for off Horn’s Reef Nephrops. Generic technical measures for the North Sea
include an EU minimum landing size for Nephrops of 25mm carapace length.
Nephrops landings from off Horn’s Reef are predominantly made by Danish and German vessels with some landings taken by the
Netherlands and Belgium. Surveillance activities to record compliance with national and international fishery control measures are
primarily the responsibility of the competent fishery inspection authorities in each country. The requirements for surveillance and
sanctions for infringements are laid down in the EU Control Regulation (EC) No 1224/2009. Surveillance activities on the off Horn’s Reef
fishery include the use of vessel monitoring systems (VMS) on vessels over 12m overall length; an electronic reporting system (ERS), and a
vessel detection system (VDS).
In Denmark, the Danish AgriFish Agency and Navy as well as the German Federal coastguard and Navy are variously responsible for
surveillance activities using patrol vessels and/or aerial patrols, inspection of vessels, gear and catches at sea and on shore, and
verification of EU logbook data against sales documents. The EU Control Regulation specifies that Member States should set up electronic
databases containing the inspection and surveillance reports of their officials as well as records of infringements and records of purchases
and sales. Since implementation of the regulation, reporting has subsequently improved with more widespread use of electronic logbooks
and reduction in vessel length for mandatory VMS deployment from 15m to 12m.
Data collection, notably of discard information, for this area, is somewhat limited, inferring potential for non-compliance, however when
considering the system of enforcement measures in place and that as an offshore fishery, that most of the fishing is by larger vessels,
surveillance can probably be considered moderately effective.
Eventual implementation of the Landings Obligation rules (EU 1380/2013) may affect harvesting practices. Although ICES advised for the
first time this year based on both implementation and non-implementation of the rules with respect to Nephrops, it remains to be
ascertained what secondary effects may derive from the requirement to land bycatch of quota finfish species.
References
ICES. 2014a. Report of the ICES Advisory Committee 2014. ICES Advice, 2014. Book 6.
ICES. 2015. Report of the ICES Advisory Committee 2015. ICES Advice, 2015. Book 6.
Bycatch Details
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Targeting and behaviour
Demersal otter trawls targeting Nephrops operating in this area can be towed by a single boat as a single or multiple rig. Gears are
adapted to the substrate type and the species targeted, with a relatively narrow range of conditions in which they can operate. Generally
the sweeps are shorter on Nephrops trawls than on those designed to catch fish, since unlike fish, Nephrops are not herded into the path
of the trawl.
Skippers will use information available to them to choose known tow locations within the mud patch where catch rates and catch
compositions are likely to be favourable, whilst taking into account other operational factors such as vessel size, weather, tide and fuel
costs.
Demersal otter trawling is not a well targeted fishing activity given that a wide variety of non-target species can be caught. As well as
Nephrops, this fishery catches a wide variety of mixed demersal finfish, such as Atlantic cod (Gadus morhua), haddock (Melanogrammus
aeglefinus) and whiting (Merlangius merlangus), and these mixed catches means that the minimum cod end mesh size of 80 mm and
other aspects of the management regimes and markets are not optimal for all the species caught. Fish may be discarded because they
are smaller than the Minimum Conservation Reference Size, or the size and/or species are not marketable. Discarding due to the vessel
being short of quota for the managed species also occurs.
Evidence of bycatch risk
Discard rates have been estimated from surveys at around 30-40% of total catch weight in European demersal otter trawl fisheries
(European Commission, 2011). A characteristic fish and invertebrate fauna tends to occur on Nephrops fishing grounds, however the
quantity and composition of bycatch will vary considerably between Functional Units within the North Sea. The Discards Atlas for the
North Sea demersal fisheries (Anon, 2014) shows 64% of the combined catch of the top six species taken by small mesh otter trawls (80 –
99 mm mesh size; including the category used for Nephrops ) in the North Sea during 2010-2012 was discarded. The largest amounts
discarded amongst these species were dab, plaice, whiting and haddock.
Nephrops fisheries have a small bycatch of elasmobranch species including skates, rays and sharks (particularly spurdog). These species
have a relatively large size at maturity and low numbers of young (low fecundity) and are considered more vulnerable to fishing than the
more fecund teleost (gadoid) stocks such as whiting and haddock. There are prohibitions on landing those which are most depleted. This
helps conserve stocks, because these species have good survival potential (Enever, et al., 2009).
Mitigation measures
A wide variety of non-target species are caught in European mixed otter trawl fisheries. Optimising gear selectivity in mixed fisheries is
challenging given that different species have different selectivity requirements.
Many measures have been designed and tested to increase selectivity in Nephrops trawls (Catchpole and Revill, 2008). Some have been
implemented as compulsory in the Nephrops North Sea fishery such as the use of sorting grids or 120 mm square mesh panels (EU
227/2013).
There are also measures nationally to control cod end twine thickness and design, intended to counter measures to reduce selectivity and
there is some voluntary uptake of trawl designs that have been tested to reduce discards, for example the ‘coverless’ trawl designed and
tested by Seafish (UK) and fully described in Dunlin & Reese (2003) and Revill et al. (2006).
A bycatch reduction scheme (Commission Regulation (EU) 724/2010, Norwegian Marine Fisheries Act 2008) allows real time closures of
areas has been enacted to protect juvenile gadoid (cod, haddock, saithe and whiting) when the catch rates of those juveniles becomes too
high.
The cod recovery plan (EU 1342/2008) which is in force in North Sea, Eastern English Channel, Irish Sea, West of Scotland and the
Skagerrak, has encouraged a diversity of measures to incentivise the use of more selective gear by vessels targeting whitefish with
demersal otter trawls. Effort per vessel is limited to a number of days at sea per year. Additional days at sea are available for vessels using
certain specified gears and measures, tested for their efficacy at improving selectivity.
The different European Nations have implemented different measures in their fisheries, described below are measures implemented in
the UK fisheries.
Real time closures
The cod avoidance plans also include ‘real time’ closures of areas where concentrations of cod are found. Since 2007 UK administrations
have operated these areas for UK vessels in the North Sea and English Channel in response to concentrations of juvenile cod; when a
vessel catches more than threshold number of cod per hour agreed by a boarding officer and the skipper or concentrations of adult cod
through analysis of landings and Vessel tracking data (VMS). The size and duration of the closure varies according to administrative body.
This a similar scheme to designed operated under European legislation (EU 783/2011) which is designed to protect juvenile cod, saithe,
haddock and whiting and there are also seasonal closures to protect spawning stocks (See Marine Scotland and Marine Management
organisation websites).
It has proved difficult to quantify the efficacy of each of these measures, however ‘it seems likely that cod avoidance measures have
contributed significantly to the reduction in the discard rate of cod’ in the North Sea fishery (Anon, 2014).
Landings obligation
The introduction of the landings obligation or ‘discard ban’ under the EU Common fisheries policy (EU 1380/2013) is intended to take place
over the period 2016 – 2019 in this fishery. This landings obligation will ultimately apply to all species managed by TAC; it will not apply to
non-TAC species, however many of these are likely to benefit from improved selectivity.
References
Anon. 2014. Prepared by Scheveningen group, Discard Atlas for the North Sea Demersal Fisheries.
Catchpole, T. L., & Revill, A. S. 2008. Gear technology in Nephrops trawl fisheries. Reviews in Fish Biology and Fisheries, Volume 18(Issue 1),
17–31.
Dunlin, G. and Reese, R., (2003) Financial Instrument for Fisheries Guidance (FIFG) Project, An Industry-centred conservation project –
Commercial proving trials of a new prawn trawl design, SFIA, Seafish Report, 551.
Enever, R., Catchpole, T. L., Ellis, J. R., & Grant, A. 2009. The survival of skates (Rajidae) caught by demersal trawlers fishing in UK waters.
Fisheries Research, 97(1-2), 72–76. doi:10.1016/j.fishres.2009.01.001
European Commission, 2011. Impact Assessment of Discard Reducing Policies, Common fisheries policy impact assessment. EU Discard
Annex. Studies in the Field of the Common Fisheries Policy and Maritime Affairs. Lot 4:
[http://ec.europa.eu/fisheries/documentation/studies/discards/report_en.pdf] [Date accessed: 07-Jan-16]
Revill, A., Dunlin, G., Holst, R. 2006. Selective properties of the cutaway trawl and several other commercial trawls used in the Farn Deeps
North Sea Nephrops fishery. Fisheries Research, 81 (2-3), pp. 268-275
Habitat Details
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Targeting and Behaviour
Fishermen use their knowledge of seabed types and prime Nephrops grounds together with information from the vessel’s electronic
mapping tools to make informed decisions on where to trawl. Gears are adapted to the substrate type and the species targeted, with a
relatively narrow range of conditions in which they can operate. Generally the sweeps are shorter on Nephrops trawls than on those
designed to catch fish, since unlike fish, Nephrops are not herded into the path of the trawl.
Evidence of habitat risk
Nephrops grounds generally contain a range of burrowing fauna including Nephrops and species of fish and shrimps. There are some
areas inhabited by sea pens, slender colonial hydroids which protrude from the mud surface. Effectively the burrowing activities of the
fauna form a structure within which other marine life can live. The passage of trawlers’ ground gear, clumps (in the case of twin rig) and
doors over Nephrops’ burrows may close up their entrances. Provided the animals are not injured, they have been observed to be able to
open up the burrows again (Coggan, Smith, & Moore, 2001). Thus apart from the energy cost in burrow maintenance, the direct effects of
trawl passage on uncaught Nephrops may be minimal.
However, the mechanical disturbance of the gear on the seabed is likely to affect the structure of the burrowed mud community. There
have been ecological effects on benthic communities observed which have been related to the amount of Nephrops trawling over a long
period. The effects include changes in species composition and biodiversity (Hinz, Prieto, & Kaiser, 2009).
Mitigation measures
Under the Marine Strategy Framework Directive (MSFD) from the European Union (Council Directive 56/2008), Member States have
committed to aim towards ‘good environmental status’ (GES) for the seabed habitats by 2020. The Convention for the Protection of the
Marine Environment of the North-East Atlantic (the ‘OSPAR Convention’), which was signed up to by 15 nations including Norway plus the
European Union, is developing a coherent network of Marine Protected Areas to protect vulnerable marine habitats in the North-East
Atlantic and the development of related areas under the European Habitats Directive (Council Directive 43/1992) contributes to this
process as does the UK Marine Act and Marine Scotland Act designating Marine Protected Areas in UK waters.
These initiatives have resulted in improvements in habitat mapping and risk assessment of the effects of trawling on the seabed as well as
measures to implement management measures where sites are considered at risk.
Two MPAs have been designated within the ICES rectangles containing the off Horn’s Reef FU, the Sydlige Nordsø MPA (Denmark) and the
Sylt.Aussenr.-Oestl.Dt.Bucht MPA (Germany). The designation for the Danish MPA lists sandbanks which are slightly covered by sea water
all of the time as its protected habitat whilst the German MPA lists the same such sandbanks as well as reefs as its. The footprint of the
fishery is unlikely to overlap with protected areas and thus should not be impacting any sensitive features, however species distribution
information for both sites is as yet incomplete, with the potential that the fishery may still be impacting protected-status species. Once
more complete information is obtained, spatial management measures may then be implemented at these sites.
References
Coggan, R. A., Smith, C. J., & Moore, P. G. (2001). Final report; Comparison of rapid methodologies for quantifying environmental impacts
of otter trawls Final report DG XIV Study Project 98/017 (p. 254).
Hinz, H., Prieto, V., & Kaiser, M. J. (2009). Trawl disturbance on benthic communities: chronic effects and experimental predictions.
Ecological Applications : A Publication of the Ecological Society of America, 19(3), 761–73.
[http://www.ncbi.nlm.nih.gov/pubmed/19425437] [Date accessed: 31-Jan-15]
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